Berlin 2015 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 89: Inorganic/Organic Interfaces: Molecular Switches
O 89.1: Vortrag
Donnerstag, 19. März 2015, 15:00–15:15, MA 043
Electronic and Thermal Fluctuations of Functional Molecules on Metals — Reinhard Maurer1,2, Wei Liu3, Igor Poltavskyi3, Thomas Stecher2, •Harald Oberhofer2, Alexandre Tkatchenko3, and Karsten Reuter2 — 1Yale University, New Haven, USA — 2Technische Universität München, Germany — 3Fritz-Haber Institut der Max-Planck-Gesellschaft, Berlin, Germany
The prevailing working hypothesis in vacuum surface science is that finite-temperature effects do not significantly alter the equilibrium properties of molecules adsorbed to surfaces. In this work, we show this not to be the case for the adsorption geometry, energetics, and desorption temperature of the molecular switch Azobenzene on Ag(111). Comparing to X-ray standing wave measurements and temperature programmed desorption experiments, we find strong discrepancies to static Density-Functional Theory calculations. We overcome these through anharmonic corrections and explicit ab initio molecular dynamics simulations of the free energy of desorption to account for the thermal fluctuations. Additionally, inclusion of many-body dispersion effects accounts for the electronic fluctuations that govern the interaction strength. With respect to both, our calculations show that more modest, prevalent approaches fail to capture the sizable entropy of desorption and therewith the correct desorption temperature. An accurate description of adsorbate interactions and entropies of adsorption in functional hybrid metallic-organic systems thus necessitates a full account of the inherent anharmonicity of adsorbate and substrate, in addition to an accurate description of dispersion interactions.